quote:

ORIGINAL: speedracerntrixie

Lighter is always better. The old argument that a heavier airplane is better in high winds is hogwash. It just means the airplane is poorly set up and reacts poorly to airspeed variations. Wind = airspeed variations.

quote:

ORIGINAL: speedracerntrixie

Lighter is always better. The old argument that a heavier airplane is better in high winds is hogwash. It just means the airplane is poorly set up and reacts poorly to airspeed variations. Wind = airspeed variations.

quote:

ORIGINAL: Speedy-Gonzales

I'm going to throw some physics at you all here and try not to cause pandamonium. If you don't agree with it then so be it.

OK....here goes it!

800 sq/in. is the breaking point to being able to fly with higher wing loadings but wing geometry also starts to come into play. You must start considering things like washout in the outer wing panels and flaps since angle of attack changes during takeoff,landing, and SLF. Also application of power changes during these stages of flight.

There is also a very interesting study ,as many of you know, concerning ''Reynolds numbers'' when calculating how much you can load a wing and still maintain good flying characteristics. One of the points I found very interesting is that the actual wing area is not the only factor when calculating the loading or lifting capabilities of a wing. The wing's ''VOLUME'' is to be considered. Meaning.....how much volume does the wing displace in the air. This would be like filling up your bathtub and submerging a sealed or solid object ( i.e. your wing ) into the water to measure the volume it displaces in the water.

This is why a Boeing 747 can weigh and lift the incredible loads that it does comparred to the marginal lifting capability of even a giant RC model. If you don't agree with my use of the word ''marginal'' then put a brick in your model next time you fly it and see what a difference it makes.

Here it is in much simpler terms:

For a 1/4 scale model to be able to lift 1/4 of the actual weight of the full scale aircraft the molecules of the air would have to be 4 times as dense ( see examples below ). As wing area and volume increase there is a ''snowball'' effect thus my comment on the 800 sq/in. as being a breaking point for increased wing loadings. The density of air molecules is constant unless we are talking flight at higher altitudes.

1/3 scale= 3x air density
1/4 scale= 4x air density
1/6 scale= 6x air density
1/8 scale= 8x air density


Care to dig deeper? Go here:

http://www.grc.nasa.gov/WWW/K-12/airplane/reynolds.html


To put all this in understandable terms....YES!....Lighter is better for model aircraft.

I'm not that smart but I did stay at a ''Holiday Inn Express'' last night!

quote:

ORIGINAL: speedracerntrixie

Lighter is always better. The old argument that a heavier airplane is better in high winds is hogwash. It just means the airplane is poorly set up and reacts poorly to airspeed variations. Wind = airspeed variations.

quote:

ORIGINAL: Speedy-Gonzales

I'm going to throw some physics at you all here and try not to cause pandamonium. If you don't agree with it then so be it.

OK....here goes it!

800 sq/in. is the breaking point to being able to fly with higher wing loadings but wing geometry also starts to come into play. You must start considering things like washout in the outer wing panels and flaps since angle of attack changes during takeoff,landing, and SLF. Also application of power changes during these stages of flight.

There is also a very interesting study ,as many of you know, concerning "Reynolds numbers" when calculating how much you can load a wing and still maintain good flying characteristics. One of the points I found very interesting is that the actual wing area is not the only factor when calculating the loading or lifting capabilities of a wing. The wing's "VOLUME" is to be considered. Meaning.....how much volume does the wing displace in the air. This would be like filling up your bathtub and submerging a sealed or solid object ( i.e. your wing ) into the water to measure the volume it displaces in the water.

This is why a Boeing 747 can weigh and lift the incredible loads that it does comparred to the marginal lifting capability of even a giant RC model. If you don't agree with my use of the word "marginal" then put a brick in your model next time you fly it and see what a difference it makes.

Here it is in much simpler terms:

For a 1/4 scale model to be able to lift 1/4 of the actual weight of the full scale aircraft the molecules of the air would have to be 4 times as dense ( see examples below ). As wing area and volume increase there is a "snowball" effect thus my comment on the 800 sq/in. as being a breaking point for increased wing loadings. The density of air molecules is constant unless we are talking flight at higher altitudes.

1/3 scale= 3x air density
1/4 scale= 4x air density
1/6 scale= 6x air density
1/8 scale= 8x air density


Care to dig deeper? Go here:

http://www.grc.nasa.gov/WWW/K-12/airplane/reynolds.html


To put all this in understandable terms....YES!....Lighter is better for model aircraft.

I'm not that smart but I did stay at a "Holiday Inn Express" last night!

quote:

ORIGINAL: Rob2160

quote:

ORIGINAL: speedracerntrixie

Lighter is always better. The old argument that a heavier airplane is better in high winds is hogwash. It just means the airplane is poorly set up and reacts poorly to airspeed variations. Wind = airspeed variations.

Not sure if I totally agree with this.. the foamies definately fly nicer in strong winds and turbulence when slightley heavier....  Subjectively...

The planes are set up the same and the battery location does not affect CG.. it is simply extra weight with a bigger battery, makes it more stable in severe turbulence..

Real gliders also use water ballast.. an interesting argument FOR extra weight.. 

http://www.ddsc.org.au/documents/manuals/Flying%20with%20Water%20Ballast.pdf

Steady constant winds won't change airspeed.. only the groundspeed will change.. turbulent constantly changing wind will give airspeed variations for sure.

What do you mean by "Reacting poorly to airspeed variation"

Just didn't quite understand what you mean't ... what is a "poor reaction"

quote:

ORIGINAL: JohnBuckner

Its a safe bet that lite flys better and crashs better. The later is always a factor unless your one that bins an airplane for minor damage.

As far as manufacturers go, most if not all have learned to fib a bit since they have learned Lite not only flys better and crashs better but Lite sells better as well, thats a fact

John

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Some of you may have heard about the Extreme Flight 78" Extra. It is very light, intended for either electric or small gassie, around 30cc. The model usually "assembles" (it's an ARF so not really built by me) to around 12 pounds. It's a big plane for 12 pounds. The Chinese factory where it is being built does a good job with both weight and accuracy

Anyway, a couple years ago I decided to put a piped DLE55 in it. With some careful planning and a redo of the engine box and landing gear, I added a soft mount and the piped DLE and picked up only about 4 ozs extra. The point is that at 12 pounds 4 ozs and a DLE55 up front, some might think this is not a good thing and the engine might fly clean off the model. NOT SO!! It flew great with its 35 pounds of thrust give or take.

The major take away is that most models are way overbuilt and are unnecessarily porky as a result. This was proof enough and on a Chinese built ARF no less.

After flying lightness for the better part of 2 decades, I can tell immediately when one is porky. They just don't perform as well in the air and landings can be loads of fun when they stall and fall. My Take!!

quote:

ORIGINAL: Rob2160
Real gliders also use water ballast.. an interesting argument FOR extra weight.. 

quote:

ORIGINAL: speedracerntrixie

quote:

ORIGINAL: Rob2160

quote:

ORIGINAL: speedracerntrixie

Lighter is always better. The old argument that a heavier airplane is better in high winds is hogwash. It just means the airplane is poorly set up and reacts poorly to airspeed variations. Wind = airspeed variations.

Not sure if I totally agree with this.. the foamies definately fly nicer in strong winds and turbulence when slightley heavier....  Subjectively...

The planes are set up the same and the battery location does not affect CG.. it is simply extra weight with a bigger battery, makes it more stable in severe turbulence..

Real gliders also use water ballast.. an interesting argument FOR extra weight.. 

http://www.ddsc.org.au/documents/manuals/Flying%20with%20Water%20Ballast.pdf

Steady constant winds won't change airspeed.. only the groundspeed will change.. turbulent constantly changing wind will give airspeed variations for sure.

What do you mean by "Reacting poorly to airspeed variation"

Just didn't quite understand what you mean't ... what is a "poor reaction"

Rob, let see if I can do a better job of explaining this. First lets tackle the silplane an ballast thing. Think as wing loading as potential energy. The sailplane wil convert this potential energy into kinetic energy by diving. The higher the potential energy ( to a degree ) the less degree of a dive is required to maintain the optimum airspeed for the particular airfoil. This is refered to as L/D. You have no doubt seen this while flying your foamies.


Ok now power airplanes and more specific aerobatic and race planes that I have most experience with. A properly trimmed airplane will recat to the wind less because all the peices of the puzzle are working together. The result is what I call ' Wind Damping "  A simple example of this is an airplane that is set up nose heavy and carrying some up trim. As the airplane is flying into the wind and the wind speed increases, the up trim becomes more effective and the airplane ballons. The opposite happens when the gust dissipates.

quote:

ORIGINAL: JohnBuckner

Rob first water ballast in high performance sailplanes is not the norm and not all sailplanes use this in fact it is in the minority. It is not a good argument for extra weight in our models.

Ballast is caried for one reason and that is to increase speed between the boomers (thermals) on a cross country flight. In fact it is seldom carried if no cross country is contemplated.

The L over D or glide ratio is improved with the ballast but with payoff of greater minimum sink. So while it does alter the character of performance it is really only good for decreasing the time between the boomers and this has no practical purpose in our typical RC flight and the way we fly our models.

Back in the seventies there was a wonderful informal event every year at Bishop Ca. in November simply called the Wave Camp and was a gathering of all sorts of sailplanes that lasted about a week. Most years the elusive waves never materialized and we spend most of the time flying each others aircraft. My contribution was my Fournier RF-4d motorglider which was quite popular and my ship got lots of publicity of the time as this event was heavily covered by the popular aviation press of the time.

I did get some fantastic flight in in several high performance glass ships that has water ballast but it was seldom used, that included if my memoriy is correct an open class Cirrus and Diamant, this was a very long time ago.

My favorite however was Peter Lerts German wood Zugfolgel (spelling) which was one of the last high performance wood ships.

The usage of water ballast in some high performance full scale has no paralell because of the way we fly our airplanes and is not a reasonable argument for heavy airplanes.

The only reasonable exception is possibly some forms of RC Ridge soaring or dyanmic soaring.

John

quote:

ORIGINAL: GerKonig

I have a electric Telemaster 72'' wingspan that flies better with the 4 cell pack than the 3 cell. The 4 cell is heavier. BUT when for fun I installed some giant balloon tires (to look like a bush plane), I compensated the CG shift, but it DID NOT LIKE IT. The additional weight did not help at all... Had to put the light tires back. So, my take is that there is a limit, but in general light is better.

A 80'' warplane that weights 30 pounds is a really good ''wind penetrator'' almost as good a a brick...

I remember the old times when I had a buddy that liked to build scale 60 size warplanes. He used to glass them, and over paint, and add details. They were legit led sleds, with a narrow flight envelope like: Max speed 72 mph, cruise speed 70 mph stall speed 68 mph... all his models had retracts, one landing, and the landing gear was gone. Not easy to be heavy, and have to come in hot, and make a nice landing on grass using small wheels (scale).

Gerry

quote:

ORIGINAL: ARUP
Lighter flies better and crashes better.

quote:

Maximizing average speed

Soaring pioneer Paul MacCready is usually credited with developing mathematical principles for optimizing the speed at which to fly when cross-country soaring,[49]:11-10 although it was first described by Wolfgang Späte in 1938.[50] The speed to fly theory allows the optimal cruising speed between thermals to be computed, using thermal strength, glider performance and other variables. It accounts for the fact that if a pilot flies faster between thermals, the next thermal is reached sooner. However at higher speeds the glider also sinks faster, requiring the pilot to spend more time circling to regain the altitude. The MacCready speed represents the optimal trade-off between cruising and circling. Most competition pilots use MacCready theory to optimize their average speeds, and have the calculations programmed in their flight computers, or use a "McCready ring", a rotatable bezel on the glider's variometer to indicate the best speed to fly. The greatest factor in maximizing average speed, however, remains the ability of the pilot to find the strongest lift.[23]:56

On cross-country flights on days when strong lift is forecast, pilots fly with water ballast stored in tanks or bags in the wings and fin. The fin tank is used to reduce trim drag by optimizing the center of gravity, which typically would shift forward if water is stored only in the wings ahead of the spar.[49]:5-13 Ballast enables a sailplane to attain its best L/D at higher speeds but slows its climb rate in thermals, in part because a sailplane with a heavier wing loading cannot circle within a thermal as tightly as one with a lower, unballasted wing loading. But if lift is strong, typically either from thermals or wave, the disadvantage of slower climbs is outweighed by the higher cruising speeds between lift areas. Thus, the pilot can improve the average speed over a course by several percent or achieve longer distances in a given time.[23]:63 If lift is weaker than expected, or if an off-field landing is imminent, the pilot can jettison the water ballast by opening the dump valves.[23]:64

On days with particularly strong and widespread lift pilots can attain high average speeds by alternating periods of fast flight with pull-ups, merely slowing down in areas of lift without deviating from the course. This 'dolphining' technique can result in high average speeds because the height lost can be minimised until particularly strong lift is encountered when circling would be most effective.